Modelling infiltration and infiltration excess: The importance of fast and local processes

Abstract

Physically based distributed hydrological models aim at an adequate representation of hydrological processes, including runoff generation. A significant proportion of runoff is generated through the subsurface, that is, by groundwater flow or unsaturated subsurface stormflow. However, in the case of high rainfall intensity and/or low soil-surface infiltrability, surface runoff may strongly contribute to total runoff, too, either through saturation excess ("Dunne-type surface runoff") or infiltration excess ("Hortonian surface runoff"). Both types of surface runoff can be rather important if antecedent wetness is high and parts of the catchment area are saturated (leading to saturation excess), or if the maximum infiltration rate into the soil surface is less than the actual rainfall intensity (resulting in infiltration excess). Even though the latter process can be very important during high-intensity rainstorms, both for flood generation and for matter transport linked with surface runoff, an appropriate consideration of this process in catchment models is still challenging.Actually, budgeting between the actual rainfall intensity and the soil surface infiltration capacity is required and there are a number of challenges in the details: First, the "real" rainfall intensity may vary tremendously in time increments much smaller than the time step of the model. The soil surface infiltrability can also be significantly reduced, for example, by crusting, compaction or sealing of the soil surface or through hydrophobic effects. Otherwise, soil infiltrability can be strongly enhanced as a consequence of preferential flow paths/macropores caused by, for example, bioturbations or other voids. Finally, there is a high variability of such soil surface features at a small spatial scale, below the typical spatial modelling unit. We present observational data and approaches to deal with these challenges. We show results from combined infiltration/infiltration-excess experiments and observations at three spatial scales. Then, we present a model approach based on a double-porosity soil enabling the combined modelling of high infiltration rates and dampened soil moisture distribution after termination of infiltration, as observable in the field. Furthermore, we present an approach to model the effects of soil surface conditions on actual infiltration capacity. These approaches improved the plausibility and explanatory power of the model concerning surface runoff generation and soil moisture

Towards more credible models in catchment hydrology to enhance hydrological process understanding: Preface

“…The results from catchment scale show that the macropore based approach is more robust in reproducing flood hydrographs for different rainfall intensities and generally outperforms the modelling approach without macropores. Altogether Bronstert et al (2023) conclude that macropores are of high relevance for infiltration and soil moisture dynamics during periods of high intensity rainfall and therefore should be considered in catchment modelling focusing on simulation of flood events.…”

“…The study by Bronstert et al (2023) focuses on description of infiltration excess (Hortonian surface runoff) in catchment models. In particular, they investigate the importance of micro-and macropores in the infiltration process.…”

Natural Hazards in a Changing World: Methods for Analyzing Trends and Non‐Linear Changes

“…Besides the possible impacts of climate change, the consequences or land-use change, modifications of the river network, or water resource management may significantly alter river runoff and hydro-extremes (Bronstert et al, 2007(Bronstert et al, , 2023Niehoff et al, 2002;Pfister et al, 2004). Particularly in high mountain regions, reservoirs for hydropower production affect river runoff, redistributing river runoff from summer to winter and thus decreasing runoff seasonality (Arheimer et al, 2017;Bosshard et al, 2013;Meile et al, 2011;Pérez Ciria et al, 2019;Verbunt et al, 2005).…”

Rhine flood stories: Spatio‐temporal analysis of historic and projected flood genesis in the Rhine River basin

“…In the latter, we distinguish in particular the river runoff due to snowmelt and the runoff due to liquid precipitation that is, rain. Further detailing of flood‐forming hydrological processes on and below the ground surface may be important, for example, for specific land surface runoff issues (Bronstert et al, 2023; Hundecha & Bárdossy, 2004; Niehoff et al, 2002), however, for the case of large river basins, where both pluvial and nival runoff generation may occur, the question of the extent, spatial origin, and timing of snowmelt and rain‐induced runoff has prior importance for flood genesis. Therefore, in this study, we focus on the flood generation on the catchment scale and investigate the spatio‐temporal distribution of rainfall, snowmelt and discharge generated.…”